The present invention relates to machine tool design, fabrication and, more specifically, to the composition and microstructure of a specialized material for machining titanium or a titanium alloy.
Titanium alloys are widely used in the aerospace industry because of their superior mechanical properties. Unfortunately, titanium and titanium alloys are very difficult to machine. In fact, the machinability of these materials has become the most significant process limitation in manufacturing many aerospace related components.
Typically, titanium and titanium alloys cannot be machined at high cutting speeds ( greater than 200 m/sec) because they have low thermal conductivity and high work-hardening characteristics. As a result, cutting temperatures typically rise rapidly to 1100xc2x0 C., even at low cutting speeds ( less than 50 m/min) and associated production is time consuming and costly.
Many ceramic machining materials have proven to be ineffective in machining titanium or titanium alloys because of their high degree of reactivity with titanium. As a result, there are few viable alternatives to conventional cemented carbide machine tool materials for titanium or titanium alloy machining and there is a continuing need for a material that may be utilized to achieve effective, high speed machining of titanium or titanium alloys.
This need is met by the present invention wherein a machine tool material is provided comprising a yttrium aluminum garnet matrix material and a reinforcing material uniformly dispersed in the matrix material. In accordance with one embodiment of the present invention, a machine tool material is provided comprising a matrix material and a reinforcing material. The matrix material comprises a yttrium aluminum garnet (YAG). The reinforcing material is uniformly dispersed in the matrix material. The matrix material and the reinforcing material are present in proportions selected such that the machine tool material is substantially resistant to transfer of impurities to Ti or a Ti alloy, by way of either chemical reaction with or diffusion into the Ti or Ti alloy material to be machined. The matrix material preferably comprises Y3Al5O12. The reinforcing material may comprise SiCw, TiC, TiN, TiB2, or combinations thereof.
The matrix material and the reinforcing material are preferably present in proportions selected such that the machine tool material is resistant to the transfer of impurities through chemical reaction with or dissolution into Ti or a Ti alloy. Preferably, the machine tool material is characterized by a low solubility in Ti, or a Ti alloy and defines a thermodynamically stable phase at temperatures up to about 1200xc2x0 C.
The reinforcing material preferably comprises a material present in a proportion selected to enhance the characteristic electrical conductivity of the machine tool material and enable electrical discharge machining of the machine tool material. The reinforcing material is also preferably provided to enhance the hardness and the fracture toughness of the matrix material. By way of illustration and not by way of limitation, it is noted that measured properties of a sample material yielded flexural strength values of about 650 to about 750 MPa and fracture toughness values of about 4.15 to about 4.2 MPa(mxc2xd) and about 5.45 to about 5.5 MPa(mxc2xd).
In accordance with another embodiment of the present invention, a machine tool material is provided comprising a matrix material and a reinforcing material. The matrix material comprises a yttrium aluminum garnet and the reinforcing material comprises a material present in proportions selected to enhance the characteristic electrical conductivity of the machine tool material. Preferably, the electrical conductivity is enhanced to an extent sufficient to enable electrical discharge machining of the machine tool material.
In accordance with yet another embodiment of the present invention, a machine tool is configured to cause frictional engagement of a workpiece and a workpiece machining element as the workpiece and the machining element move relative to one another. The workpiece machining element is formed of a machine tool material comprising a matrix material and a reinforcing material. The matrix material comprises a yttrium aluminum garnet. The reinforcing material is uniformly dispersed in the matrix material. The matrix material and the reinforcing material are present in proportions selected such that the machine tool material is substantially resistant to transfer of impurities through chemical reaction with or diffusion into Ti or a Ti alloy to be machined.
Accordingly, it is an object of the present invention to provide a material for effective, high speed machining of titanium or titanium alloys. Other objects of the present invention will be apparent in light of the description of the invention embodied herein.